This invention is generally related to generating acoustic and seismic signals.
U.S. Pat. No. 5,125,317 discloses a seismic generator designed for a mine-clearing vehicle. This generator has a motor driving an unbalanced disk. This causes vibrations as the motor rotates. The generator is mounted near a vehicle axle and the vibrations are transmitted to the ground through the axle.
The main drawback of such a device is that it generates only one vibrational frequency (unimodal system). Hence it is not possible to simulate the entire frequency band generated by an actual vehicle, unless several generators with different frequencies are combined, which would be expensive and difficult to install in the vehicle. A single system of this type would not effectively clear modern antitank mines which have seismic sensors able to analyze the vibrational signal received. Moreover, the ratio between the power necessary to drive the motor and the power of the seismic/acoustic signals obtained is very low, mainly because the signals have to pass through the gear train of the vehicle, which adds interference to the initial signal. Hence the efficiency of such a device is low.
French Patent 2,748,560 discloses a mine-clearing system for triggering land mines placed, buried, or disposed at the side of the road. This system produces a seismic signal from its own drive wheels that have appropriate shapes.
This system has drawbacks as well. First, the power of the signal depends on the weight supported by the wheels, hence the weight of the carrying vehicle. Such a device cannot be implemented on a small remote-operated vehicle without a sharp efficiency loss. Moreover, the signal generated is once again unimodal and depends on the rate at which the vehicle moves; no signal can be generated when it is at rest.
It is also known, in particular from French Patent 914,284, that mines can be cleared by using weights attached to the ends of cables driven by a rotating drum. The goal of these devices is not to deceive an acoustic or seismic sensor but to cause buried mines to explode by impact.
In an area totally different from mine-clearing, U.S. Pat. No. 4,005,795 proposes a device for seismic prospecting from a ship. This device uses a drum with weights that strike an anvil that transmits the impacts thus produced to the hull of the ship. The weights are irregularly distributed around the drum to ensure generation of a random seismic signal. This randomness is necessary for implementing undersea prospecting processes and is unsuitable for a land mine-clearing application.
This invention provides systems and methods for generating acoustic and seismic signals that enable generation of seismic signals composed of several readily modifiable frequencies. The systems and methods according to the invention thus enable the seismic signature of an actual vehicle to be simulated. The systems and methods according to the invention also supply a high-power seismic signal whose frequency does not depend on the speed of the vehicle carrying it.
According to various exemplary embodiments of the invention, a system for generating acoustic and seismic signals designed to clear mines equipped with acoustic and/or seismic sensors includes at least one drum driven rotationally by a drive, to which drum at least one weight is attached by a fastening device positioning the weight at a distance from the drum, the weight striking the ground periodically as the drum rotates to generate an acoustic and seismic signal whose period is the same as that of the striking period of the weight.
In a first exemplary embodiment of the system according to the invention, the generator has at least a first group of weights attached to the drum with a regular distribution producing a first angular distance between two adjacent weights of the first group so that, by striking the ground, this first group generates an acoustic and seismic signal with a first frequency.
In a second exemplary embodiment of the system according to the invention, the generator has at least one second group of weights attached to the drum with a regular distribution producing a second angular distance between two adjacent weights of the second group and/or between a first weight in the first group and a first weight belonging to the second group, so that when the weights strike the ground an acoustic and seismic signal with a second frequency is produced.
The drum has grooves with regular angular spacing on its outer surface for connecting the fastening devices according to different angular distributions. The fastening devices have at least one connector cooperating with one of the grooves of the drum and at least one arm at the end of which the weight is attached.
According to various exemplary embodiments of the invention, the arm can have at least one chain or at least two articulated bars, the weight or weights can have at least one rotating wheel, and the signal generator can have at least two weights with different masses.
According to other various exemplary embodiments of the invention, a method for generating a seismic and acoustic signal for clearing mines equipped with acoustic and/or seismic sensors, the signal having at least one frequency and being generated by several weights striking the ground, includes fastening at least one weight to a drum at a distance from the drum and rotationally driving the drum near the ground, wherein the at least one weight strikes the ground periodically as the drum rotates to generate an acoustic and seismic signal whose period is the same as the striking period of the at least one weight.
Advantageously, this method can be adapted to generate a signal having at least two different frequencies, wherein the weights are made integral with the drum by fastening the weights at a distance from the drum at an angular distribution around the drum so that there are at least two groups of weights at at least two different angular distances on the drum, the drum is driven rotationally near the ground at a rotational speed such that the periodic impacts of the weights on the ground generate the signal.
In a first exemplary embodiment of the method according to the invention, the method also includes analyzing the frequency of the seismic signal to be simulated, determining at least two main frequencies of the signal and of the energies associated with these frequencies, determining a weight distribution in terms of mass and location on the drum to generate such a signal, and attaching the weights to the drum by the fastening devices with the determined angular distribution.
In a second exemplary embodiment of the method according to the invention, the rotational speed for the drum can be determined, then the drum can be driven rotationally in the vicinity of the ground at the determined rotational speed such that the periodic impacts of the weights on the ground generate the signal.